With the development of technology, it has become possible to produce various types of items in various ways. For example, in the past, cutting or grinding could produce an item having a desired shape. Alternatively, a so-called plastic injection method in which a liquid material such as a liquid plastic is injected into a metal mold consisting of various materials, and then cooled and injected to form a part is also utilized. In particular, recently, a so-called computerized numerical control (CNC) method of producing an item using a numerical control machine equipped with a microprocessor has been introduced to mass-produce various items.
Meanwhile, to cope with population growth and market growth, manufacturers who manufacture items have faced the challenge of producing a variety of items at low cost. In particular, as the use period of various products becomes shorter, the time required to equip the mass production facility of the item becomes shorter. Herein, another challenge for manufacturers with rapid mass production is to maintain the yield of the produced items. In the period when the product was produced by the handicrafts, the workers performed and controlled all the production work directly. Thus, despite the design of the same item, it was impossible to maintain the quality of the item to be consistent due to various environmental factors such as the worker's skill level and fatigue. Meanwhile, since the era of large-scale automatic production by machines has been achieved, uniformity in manufacturing has been able to be gained to a great extent. However, inspection of various mechanical errors and item failures occurring in the production and assembly process of each item are not only costly because the methods used by the workers are still done by the naked eye, but also still have a problem that the consistent standard of judging the quality of products may not be applied due to the skill or fatigue of individual workers or the difference of individual standards as with the problems in the age of production of handicraft products.
In addition, consumers' standards for quality are increasing day by day. Thus, in producing items, manufacturers are also devoting efforts to eliminate defective items in the production and assembly process of the item, intermediate process and final assembly completion process. As part of this effort, in the assembly process, it is one technical challenge to determine whether the item meets the reference quality by using various inspection equipment, and pre-remove intermediate assemblies deemed to be of poor quality, so that high and uniform quality for the finished product is maintained and a high yield is obtained.